# How to Build a CapEx Forecast

*Alex Tapio · 2026-08-12 · 13 min · FP&A*

Canonical: https://finamodel.com/blog/capex-planning-and-forecasting

Learn how to build a capex forecast in Excel: top-down vs. bottom-up methods, a project-level portfolio build with NPV and payback screening, a monthly budget tracker, and a full worked example.

**A capex forecast projects how much a company will spend on long-lived assets, when the cash actually goes out, and whether each dollar clears its return hurdle. This guide covers both ways to build one - a fast top-down percent-of-revenue method for long-range models, and a rigorous bottom-up, project-by-project build for capital allocation - with a full worked example: a four-project portfolio, a monthly outlay schedule, NPV and payback screening, and a budget tracker that shows exactly where overlapping projects squeeze a spending envelope.**

Capex is the line item most financial models get wrong by simplification. A DCF or 3-statement forecast will often reduce an entire year of capital spending to a single percent-of-revenue assumption - reasonable for a long-range valuation, useless for a CFO trying to figure out whether the company can actually afford to fund six capital projects in the same quarter. The two problems are related but distinct: one is about *how much* capital a business needs to sustain and grow itself, the other is about *which specific projects*, funded *when*, clear the bar and fit inside the budget.

```mermaid
flowchart TD
    A["Need a capex forecast"] --> B{"What's it for?"}
    B -->|"Long-range model DCF, 3-statement"| C["Top-down: Capex % of Revenue"]
    B -->|"Capital allocation, board approval"| D["Bottom-up: Project-by-project build"]
    D --> E["Classify: Growth vs Maintenance Capex"]
    E --> F["Estimate cost, start month, build duration"]
    F --> G["Screen economics: NPV, payback, ROI"]
    G --> H["Spread monthly outlay over build window"]
    H --> I["Check against budget envelope"]
    C --> J["Roll into cash flow and PP&E forecast"]
    I --> J
```

*Two ways to forecast capex: a fast top-down ratio for long-range models, or a bottom-up project build for capital allocation decisions - both ultimately feed the same cash flow and balance sheet forecast.*

---

## Method 1: Top-Down - Capex as a Percentage of Revenue

When you're building a DCF, a 3-statement model, or any forecast where capex is a supporting assumption rather than the main event, the fastest defensible method is to tie it to revenue:

```
Capex = Revenue x Capex % of Revenue
```

The ratio itself should come from the company's own trailing 2-3 year average, adjusted for anything structurally changing (a new facility coming online, a shift to a more asset-light model). Typical ranges by sector:

| Sector | Typical Capex (% of Revenue) |
| :--- | :---: |
| Software / SaaS | 2-4% |
| Professional services | 1-3% |
| Consumer / retail | 3-6% |
| Manufacturing / industrial | 8-15% |
| Telecom / utilities / airlines | 15-25%+ |

```excel
// Capex as % of Revenue (assumption on B16, Revenue on row above)
= Revenue * Assumptions!$B$16
```

This is exactly the shortcut used in a [DCF model](/blog/dcf-model-excel-tutorial) to get from EBIT to unlevered free cash flow - it's fast, it's defensible for a 5-year projection, and it deliberately says nothing about which projects the money is going toward or when in the year the cash actually leaves. For that level of detail, you need the bottom-up method.

---

## Method 2: Bottom-Up - A Project-Level Capital Plan

When the question shifts from "how much capex should we assume" to "which of these eight projects do we actually fund, and can we afford all of them at once," you need a portfolio-level model built from the ground up. A working version needs four linked pieces:

1. **Project register:** Each candidate project with total cost, start month, build duration, useful life, and expected annual cash benefit.
2. **Monthly outlay schedule:** Each project's total cost spread across its build window.
3. **Economics screen:** NPV, simple payback, and ROI per project, tested against a hurdle rate.
4. **Budget tracker:** The monthly schedule rolled up against a spending envelope, with variance and running headroom.

As with any FP&A model, the discount rate, hurdle thresholds, and envelope all belong on a single assumptions block - never hardcoded into a project row - so the entire schedule reflows the moment a project slips a month or the envelope tightens.

---

## Growth Capex vs. Maintenance Capex

Before a project even reaches the register, classify it:

- **Maintenance capex:** Keeps existing operations running at their current level - equipment replacement, IT refresh cycles, compliance-driven upgrades. It's effectively non-discretionary; a business that skips it isn't saving money, it's deferring a cost that usually comes back larger (a breakdown, a compliance failure, a rushed replacement at a worse price).
- **Growth capex:** Expands capacity or capability - a new facility, a new product line, a system rollout tied to an expansion plan. It's discretionary and should clear a return hurdle before approval.

The distinction matters for two reasons. First, subtracting only maintenance capex from EBITDA gives a cleaner read on distributable cash flow than subtracting total capex, which conflates "cost of staying in business" with "investment for more business." Second, mixing the two on one dashboard without a category tag makes the NPV screen misleading - nobody expects a positive NPV on a roof replacement, but everybody should expect one on a new production line.

---

## The Core Mechanic: Spreading Capex Over the Build Window

A project's total cost rarely lands as a single lump sum. Construction, procurement, and implementation stretch spend across several months, and that timing is what actually determines whether a project fits inside a given month's budget envelope. The standard approach spreads cost evenly across the build window:

```
Monthly Outlay = Total Capex / Build Duration (months), active from Start Month through Start Month + Duration - 1
```

```excel
// Monthly outlay turns on at the start month and off after the build window closes
= IF(AND(MonthNumber >= StartMonth, MonthNumber < StartMonth + Duration), TotalCapex / Duration, 0)
```

This is a simplification - real projects often front-load or back-load spend - but an even spread is the standard planning assumption because it's auditable and it's what surfaces the real problem: when two or three projects' build windows overlap, their monthly outlays stack, and a budget envelope that looked comfortable on paper can go negative for a few months even though the annual total fits fine.

<!-- template:capex-planning -->

---

## Worked Example: A Four-Project Capex Portfolio

Assume a company is screening four candidate projects for the coming year, with a monthly capex envelope of $500,000 (a $6.0M annual budget) and a 10% discount rate:

| Project | Total Capex | Start Month | Build Duration | Useful Life | Annual Cash Benefit |
| :--- | :---: | :---: | :---: | :---: | :---: |
| A - Warehouse automation | $1,200,000 | 1 | 4 mo | 5 yrs | $350,000 |
| B - ERP system upgrade | $900,000 | 2 | 3 mo | 4 yrs | $220,000 |
| C - Fleet replacement | $600,000 | 5 | 2 mo | 6 yrs | $150,000 |
| D - Facility expansion | $2,400,000 | 6 | 6 mo | 10 yrs | $420,000 |
| **Total** | **$5,100,000** | - | - | - | **$1,140,000** |

Each project's monthly outlay is total capex divided evenly across its build window (e.g., Project A: $1,200,000 / 4 = $300,000/month for months 1-4):

| Month | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| A | 300k | 300k | 300k | 300k | - | - | - | - | - | - | - | - |
| B | - | 300k | 300k | 300k | - | - | - | - | - | - | - | - |
| C | - | - | - | - | 300k | 300k | - | - | - | - | - | - |
| D | - | - | - | - | - | 400k | 400k | 400k | 400k | 400k | 400k | - |
| **Total** | **300k** | **600k** | **600k** | **600k** | **300k** | **700k** | **400k** | **400k** | **400k** | **400k** | **400k** | **0** |

Projects A and B overlap in months 2-4, and C and D overlap in month 6 - exactly where the schedule gets tight.

### Economics Screen: NPV, Payback, and ROI

Each project's NPV uses the annual benefit as a level annuity over its useful life, discounted at 10%:

```
NPV = Annual Benefit x [(1 - (1 + r)^-n) / r] - Total Capex
```

| Project | PV of Benefits | NPV | Simple Payback | ROI | Passes Hurdle? |
| :--- | :---: | :---: | :---: | :---: | :---: |
| A | $1,326,775 | **+$126,775** | 3.43 yrs | 45.8% | Yes |
| B | $697,370 | **-$202,630** | 4.09 yrs | -2.2% | No |
| C | $653,289 | **+$53,289** | 4.00 yrs | 50.0% | Yes |
| D | $2,580,718 | **+$180,718** | 5.71 yrs | 75.0% | Yes |

```excel
// NPV using the annuity form (DiscountRate, UsefulLife, AnnualBenefit, TotalCapex as named ranges)
= AnnualBenefit * (1 - (1 + DiscountRate)^-UsefulLife) / DiscountRate - TotalCapex

// Simple payback period, in years
= TotalCapex / AnnualBenefit

// Simple ROI over the project's useful life
= (AnnualBenefit * UsefulLife - TotalCapex) / TotalCapex
```

Three of the four projects clear a positive NPV at the 10% hurdle. Project B - the ERP upgrade - comes back negative: at a $900,000 cost and only a 4-year useful life, the projected $220,000 annual benefit never earns back more than the capital charge, let alone the $900,000 itself. That doesn't necessarily kill the project (some ERP upgrades are compliance-driven, not return-driven), but it does mean it shouldn't be approved on ROI grounds alone.

**Portfolio dashboard summary:**

| Metric | Value |
| :--- | :---: |
| Total committed capex | $5,100,000 |
| Total annual benefit | $1,140,000 |
| Portfolio NPV | $158,153 |
| Average payback | 4.31 years |
| Average ROI | 42.2% |
| Projects passing NPV hurdle | 3 of 4 |
| Peak monthly capex | $700,000 (Month 6) |
| Envelope utilization | 85.0% |

### Budget Tracker: Where the Envelope Gets Tight

Rolling the monthly outlay schedule against the $500,000 monthly envelope shows exactly where overlapping projects create pressure, even though the year closes comfortably under budget:

| Month | Envelope | Scheduled | Cumulative Envelope | Cumulative Scheduled | Running Headroom | Utilization |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: |
| 1 | $500k | $300k | $500k | $300k | **+$200k** | 60% |
| 2 | $500k | $600k | $1,000k | $900k | +$100k | 120% |
| 3 | $500k | $600k | $1,500k | $1,500k | $0 | 120% |
| 4 | $500k | $600k | $2,000k | $2,100k | **-$100k** | 120% |
| 5 | $500k | $300k | $2,500k | $2,400k | +$100k | 60% |
| 6 | $500k | $700k | $3,000k | $3,100k | **-$100k** | 140% |
| 7 | $500k | $400k | $3,500k | $3,500k | $0 | 80% |
| 8 | $500k | $400k | $4,000k | $3,900k | +$100k | 80% |
| 9 | $500k | $400k | $4,500k | $4,300k | +$200k | 80% |
| 10 | $500k | $400k | $5,000k | $4,700k | +$300k | 80% |
| 11 | $500k | $400k | $5,500k | $5,100k | +$400k | 80% |
| 12 | $500k | $0 | $6,000k | $5,100k | **+$900k** | 0% |

```excel
// Running headroom on the budget tracker
= CumulativeEnvelope - CumulativeScheduled
```

Running headroom dips negative in Months 4 and 6 - exactly where Project A/B and Project C/D overlap - even though the annual envelope has $900,000 of headroom left by Month 12. This is the entire point of building a monthly tracker instead of comparing annual totals: an annual view says "we're $900k under budget," which is true and also hides two months where the company would need either a cash cushion, a short-term draw, or a one-month project slip to stay funded. Moving Project D's start from Month 6 to Month 7 would flatten both dips at the cost of finishing the facility expansion a month later - the kind of trade-off this tracker is built to surface before it becomes a cash problem.

---

## Rolling CapEx Into the Cash Flow and Balance Sheet Forecast

Once the monthly outlay schedule is set, it plugs directly into two places in the broader financial model:

- **Cash flow statement:** Monthly outlay is a cash outflow in investing activities, exactly as scheduled - this is why the monthly, not annual, view matters for a [cash flow forecast](/blog/cash-flow-forecast-excel) or [13-week cash flow](/blog/13-week-cash-flow-forecast).
- **Balance sheet (PP&E) and depreciation:** Each project's total cost adds to gross PP&E when it goes into service, then depreciates over its useful life - the same useful-life input used in the NPV calculation above also drives the depreciation schedule.

Capex forecasting doesn't stand alone - it sits alongside the other build-out-from-drivers pieces of an FP&A stack. Our guide to [financial forecasting methods](/blog/financial-forecasting-methods) covers the broader driver-based approach this plugs into, and if the capital plan is funding new capacity that also needs staffing, our [headcount planning](/blog/headcount-planning-model) guide walks through the parallel build for people costs.

---

## Common Mistakes to Avoid

1. **Treating capex as a single annual lump sum.** A project that fits comfortably on an annual budget can still blow through a monthly envelope if its build window overlaps with another project's. Model monthly, not annually.
2. **Skipping the growth vs. maintenance classification.** Without it, a dashboard mixes non-discretionary replacement spend with discretionary growth investment, making the aggregate NPV and ROI numbers meaningless.
3. **Using a single hurdle rate for every project regardless of risk.** A maintenance project and a new-market expansion don't carry the same risk profile; using one blended discount rate for both understates the return required on the riskier bet.
4. **Ignoring payback in favor of NPV alone.** A project can have a strong positive NPV over a 10-year life while tying up cash for 6 years before it's recovered - fine for a company with ample liquidity, potentially fatal for one that isn't. Screen both.
5. **Front-loading or ignoring build-window timing.** Assuming capex lands entirely in the month a project is "approved" instead of spreading it across the actual construction or implementation period misstates every monthly cash and budget check downstream.
6. **Not linking the useful life assumption between the NPV screen and the depreciation schedule.** If capital planning uses a 5-year useful life for NPV but accounting depreciates the same asset over 7, the model and the books will permanently disagree on when the investment pays for itself.

---

## Key Takeaways

- **Two methods serve two purposes.** Top-down (capex as % of revenue) is fast and right for long-range models like a DCF; bottom-up (project-by-project) is what capital allocation and board approval actually require.
- **Classify every project as growth or maintenance capex before it hits the register.** The two have different discretion, different risk, and should be screened differently.
- **Spread each project's cost across its actual build window**, not a single lump sum - that's what surfaces overlapping-project pressure on a monthly budget tracker.
- **Screen with NPV, payback, and ROI together.** NPV tells you if a project creates value at your hurdle rate; payback tells you how long cash stays tied up; neither alone is a complete picture.
- **An annual budget can hide a monthly cash problem.** The worked example closes the year $900,000 under budget while still running $100,000 over envelope in two separate months - build the tracker monthly to catch that before it happens.
- **Capex forecasting doesn't stand alone.** The same monthly schedule and useful-life assumptions flow directly into the cash flow statement, PP&E, and the depreciation schedule - keep them linked, not duplicated.

For the top-down method in context, see how capex as a percent of revenue fits into a full [DCF model build](/blog/dcf-model-excel-tutorial). For the bottom-up, project-level version with a full monthly outlay schedule, NPV screen, and budget tracker, explore the [Capex Planning template](/templates/capex-planning).


## Frequently asked questions

### What is a capex forecast?

A capex forecast is a projection of how much a company will spend on capital expenditures - long-lived assets like equipment, facilities, software, and infrastructure - over a future period, broken out by project or category and timed by month or quarter. It differs from a capex budget in the same way a forecast differs from a budget generally: the budget is the target set once a year, and the forecast is the continuously updated best estimate of actual spend, timing, and the economics (NPV, payback, ROI) behind each project. A good capex forecast feeds directly into the cash flow statement, the balance sheet (PP&E), and the depreciation schedule.

### How do you forecast capex as a percentage of revenue?

The top-down method estimates capex as a fixed or gradually changing percentage of revenue, based on the company's historical ratio or industry benchmarks: Capex = Revenue x Capex % of Revenue. Asset-light software companies typically run 2-4% of revenue; manufacturing and industrial businesses often run 8-15%; capital-intensive sectors like telecom, utilities, and airlines can run 15-25% or more. This method is fast and works well for long-range models like a DCF, where project-level detail isn't available, but it says nothing about which specific projects the spend represents or when cash actually goes out the door within the year.

### What's the difference between growth capex and maintenance capex?

Maintenance capex is spend required just to keep existing operations running at their current level - replacing worn equipment, refreshing IT infrastructure, code required to pass compliance. Growth capex is spend that expands capacity or capability - a new facility, a new product line, an acquisition-driven system rollout. The distinction matters because maintenance capex is a non-discretionary cost of staying in business (subtract it from EBITDA to get a cleaner view of distributable cash flow), while growth capex is a discretionary investment decision that should be screened against a return hurdle like NPV or IRR. Companies that don't separate the two often overstate free cash flow by treating growth spend as if it were optional, or understate return on invested capital by lumping both together.

### How do you build a capex budget template in Excel?

A working capex budget template needs four linked pieces: (1) a project register listing each candidate project with total cost, start month, build duration, useful life, and expected annual benefit; (2) a monthly outlay schedule that spreads each project's cost across its build window; (3) an economics screen computing NPV, payback period, and ROI per project against a hurdle rate; and (4) a budget tracker that rolls the monthly schedule up against a spending envelope, showing variance and cumulative headroom. The critical design rule is the same as any FP&A model: discount rate, hurdle thresholds, and the budget envelope all live on one assumptions block, not hardcoded into formulas, so the whole schedule reflows when an assumption changes.

### What's a good NPV or hurdle rate threshold for capex projects?

There's no universal number - the hurdle rate should approximate the company's cost of capital (WACC) plus a risk premium for project-specific uncertainty, commonly landing between 8% and 15% for corporate capex decisions. A project with a positive NPV at the hurdle rate is expected to create value; a negative NPV means the projected returns don't clear the cost of the capital required to fund it. Many capital committees pair the NPV screen with a simple payback ceiling (e.g., nothing over 4-5 years without an executive override) as a liquidity check, since NPV alone doesn't capture how long cash stays tied up before it's recovered.

### How does capex forecasting differ from opex budgeting?

Capex creates an asset that sits on the balance sheet and is expensed gradually through depreciation over its useful life, while opex is expensed immediately in the period it's incurred. That means capex decisions require investment-style economics - NPV, payback, ROI against a hurdle rate - because the cash goes out well before the benefit is realized, whereas opex budgeting is typically a period-by-period allocation exercise tied to a rolling or annual budget cycle. In practice the two are modeled differently but need to reconcile: a capex project's depreciation becomes an opex line, and a capex project's operating benefit (cost savings, incremental revenue) should show up in the opex or revenue forecast it was justified by.